Ultrapure polysilicon used in the electronic and solar industry is often produced through deposition from gaseous reactants via a chemical vapor deposition (CVD) process conducted within a reactor.
One process used to produce ultrapure polycrystalline silicon in a CVD reactor is referred to as a Siemens process. Silicon rods disposed within the reactor are used as seeds to start the process. Gaseous silicon-containing reactants flow through the reactor and deposit silicon onto the surface of the rods. The gaseous reactants (i.e., gaseous precursors) are silane-containing compounds such as halosilanes or monosilanes. The reactants are heated to temperatures above 1000° C. and under these conditions decompose on the surface of the rods. Silicon is thus deposited on the rods according to the following overall reaction:2HSiCl3→Si+2HCl+SiCl4.
The process is stopped after a layer of silicon having a predetermined thickness has been deposited on the surface of the rods. The silicon rods are then harvested from the reactor for further processing.
The silicon seed rods used in the reactor are formed from larger blocks or ingots of silicon that are cut by a saw to form the seed rods. The silicon seed rods typically have a circular or square cross-sectional shape. Pairs of silicon seed rods are connected in the reactor at their respective first ends by a silicon bridge rod. The opposing, second ends of the silicon seed rods are connected to a graphite chuck within the reactor.
In some systems, the first ends of the seed rods have a V-shaped or dovetail-like profile. The second ends of the rods have a conical profile to aid in connecting the ends to the graphite chuck. In these systems, an operator uses two separate machines and corresponding machining operations to machine the first and second ends of the seed rods. These machines machine the rods with a rotating grinding wheel and/or rotate the rods.
These systems suffer from a number of shortcomings, one of which is that they require two separate machines to machine one silicon seed rod. That is, one machine is required to machine the first end of the rod and a second machine is required to machine the second end. Moreover, the known systems are ill-equipped to machine rods that are not squares. For example, when the rods are cut from larger ingots into rods they may not have a true square cross-sectional shape. When such rods are mounted in a mandrel of the machines and rotated, the rotational axis of the mandrel may not coincide and instead be misaligned with the effective rotational axis of the rod. Such misalignment may result in poor-quality machining of the rod.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.